A plasma processing apparatus for processing the surface of a semiconductor substrate or the like using a plasma discharge is employed widely in the field of semiconductor manufacture. In a plasma processing apparatus, a workpiece to be processed such as a semiconductor substrate is subjected to plasma processing by producing a plasma across two electrodes (an electrode to which high-frequency power is applied and an opposing electrode to which a constant voltage is applied) provided inside a chamber. The application electrodes also are constituents of an electrostatic chuck (ESC) that holds the semiconductor substrate, etc., by an electrostatic adsorption force. More specifically, an insulating film comprising a dielectric is provided on a base serving also as an application electrode, and a workpiece such as a semiconductor substrate is placed on the film. Alternatively, an electrostatic chuck sheet in which an application electrode has been sealed in an insulating film is provided on a base and the workpiece such as a semiconductor substrate is placed on the sheet. By applying a high-voltage DC voltage to the application electrodes to cause polarization of the insulating film, static electricity is produced at the boundary with the workpiece and the workpiece is held on the base by the resulting electrostatic adsorption force (coulomb force).
In a plasma processing apparatus of this kind, it is known that local discharge (abnormal discharge) occurs at times in the plasma within the chamber. When abnormal discharge occurs, this causes damage to components in the chamber that performs the plasma discharge and a molten spray of particles attach themselves to the substrate and contaminate the same. Further, it is known that exfoliated flakes of a reaction product that has attached itself to chamber walls increases when an abnormal discharge occurs. The substrate to be processed is contaminated as a result. Furthermore, if abnormal discharge occurs on the substrate, damage to the substrate and to wiring on the substrate occurs. Thus, abnormal discharge produced in a plasma apparatus causes damage to the substrate to be processed and to apparatus itself.
Detecting abnormal discharge, therefore, is important in terms of plasma processing and several techniques for ascertaining abnormal discharge are known in the related art. For example, the specification of Patent Document 1 discloses a window-type probe having at least an electrically conductive support member provided with an opening at least in a portion of the surface thereof facing a plasma, and a dielectric member having a probe electrode in one side surface thereof disposed in the opening of the electrically conductive support member. The output end of the window-type probe is equipped with a voltage-waveform measurement unit for measuring a voltage waveform. An abnormal discharge in the plasma is detected by a change in the voltage waveform sensed by the voltage-waveform measurement unit.
Further, the specification of Patent Document 2 discloses an apparatus in which a plasma is generated in a processing chamber by a high-frequency power supply, whereby a semiconductor wafer placed in an electrostatic chuck is processed. This apparatus includes a current monitor that detects a DC current that is for actuating the electrostatic chuck, and a VDC monitor for detecting VDC level from a power supply line of a high-frequency power supply. Monitor signals from these monitors are compared by a detecting unit. Since the amount of fluctuation of each monitor signal differs depending upon the location at which abnormal discharge occurs, whether an abnormal discharge has occurred and, if so, the location thereof, can be detected by the comparison in the detection unit.
As a related technique, the specification of Patent Document 3 discloses an electrostatic adsorbing apparatus in which a workpiece to be processed is held by a desired electrostatic adsorption force and the electrostatic adsorption force can be maintained stably at a set value despite a fluctuation in a self-bias voltage. The electrostatic adsorbing apparatus forms an electric circuit in which an ammeter 144, a resistor (dielectric film) 132, a semiconductor wafer W, a plasma PR and an upper electrode 152 are connected serially between the output terminal of a variable DC power supply 146 and ground, as illustrated in FIG. 8. In order to measure the self-bias voltage, a leakage current iL that flows into the resistor 132 is detected by the ammeter 144 while the output voltage V0 of the variable DC power supply 146 is varied. Furthermore, a controller 150 adjusts the output voltage V0 of the variable DC power supply 146 in order to maintain the electrostatic adsorption force despite fluctuations in the self-bias voltage.    [Patent Document 1] Japanese Patent Kokai Publication No. JP-P2003-318115A (FIG. 1)    [Patent Document 2] Japanese Patent Kokai Publication No. JP-A-6-232089 (FIG. 1)    [Patent Document 3] Japanese Patent Kokai Publication No. JP-P2002-252276A (FIG. 2)